The present invention relates to the formation of semiconductor devices.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes, a photoresist (PR) material is deposited on the wafer and then is exposed to light filtered by a reticle. The reticle is generally a glass plate that is patterned with exemplary feature geometries that block light from propagating through the reticle.
After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the photoresist material such that a developer can remove a portion of the photoresist material. In the case of positive photoresist materials, the exposed regions are removed, and in the case of negative photoresist materials, the unexposed regions are removed. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby define the desired features in the wafer.
One problem in such processes is that microscopic photoresist structures with small widths are likely to change shape during processing. This deformation may be transferred into the film being etched, yielding etch structures, which deviate from the intended shape, dimension, or roughness. These etch-induced photoresist transformations may be classified in groups such as line edge roughening, surface roughening, and line wiggling. Line edge roughness (LER) refers to the edges of patterned lines becoming more irregular as the pattern is transferred from photoresist to the underlying film.